Nobody knows when donor sperm was first used. Naomi Cahn, a George Washington University law professor who's written a book on the fertility industry, says there are vague references going back to the 1400s.

"It's also got a very, very long history of secrecy," she said.

The first known recorded case was in 1884, when a doctor at a Philadelphia medical school inseminated a woman, under anesthesia, using sperm from his "best looking" student.

It took 25 years before the story was reported in a medical journal.

"At that time the procedure was so novel, so peculiar in its human ethics, that the six young men ... who witnest [sic] the operation were pledged to absolute secrecy," the report says.